SV1AFN Design Lab

Christophe, F1JKY, president of the French Association of Amateur Radio Relays of the Dauphine ( sent me new measurements for the modified for 30KHZ - 30 MHZ version.

Fréq (MHz)    Gain (dB)
0,05                  14
0,136                16
0,475                15,9
1,8                   16,1
3,5                   16,3
7                      16,8
14                    18,1
24                    17,4
29                    15,2
50                    6
Conso : +12V - 30mA

Thank you Christophe!

Some more photos from my measurements. 

Fig. 2 New version of PCB

​All the SMD components are factory soldered in place, you just need to wind the transformers. For T1, a larger BN43-202 or BN-73-202 can be used. KITs and ready-built modules have the BN43-2402 for the 0. 5-30 MHZ version, while the 30 KHZ - 30 MHZ versions have the BN-73-202.

2x J310 HF Pre-Amplifier Options

User Comments:

Hello I just want to let you know how pleased I am with your preamp that you modified for the LF bands. It works very well, very clean with no images. The previous preamp I was using was a Hewlett Packard and it created a lot of images down the band. I am able to receive LW stations from Europe and I live 1500km from the Canadian coast. Very impressive preamp. Terry VE3XTM Guelph ON Canada.

If you need this modification to be done in your built & tested pre-amp, just email me.

Modification for 50 KHZ to 30 MHZ (still usuable from 30 KHZ), for the users of LF bands

You need to change T1 and T2. Now, for both transformers is needed to be wound on BN73-202 dual hole cores. T1 has a primary winding of 3 turns and its secondary winding 12 turns, again center tapped. T2 now needs to have a 14 turns primary winding (center tapped) and a secondary winding of 3 turns. See the spectrogramms below. By sacrifying the upper frequency response (30-55 MHZ), you can now get a new one at 30 KHZ to 30 MHZ. This is without tweaking the feedback network.

T1 is now bigger and the PCB doesn't have enough space for it's mounting. One possible mod is to place the SMA connectors from the bottom side and by soldering the T1 primary ends directly on the input SMA pins.

Download the Schematic

A complete KIT of parts, connectors, wire as shown in the assembled PCB photo, including the gold-plated high-quality PCB is available.

The shipping is with registered mail  and tracking (your signature is required on delivery) and is not included in the price. I usually ship the next day and it takes about a week to 10 days for USA or Australia, less than a week for Europe.

KIT building Instructions

Christophe, F1JKY, president of the French Association of Amateur Radio Relays of the Dauphine ( sent me two photos with his own realization along with some test data. Notice the SMB connectors that he has used instead of the SMA.

Fréq (MHz)     Gain (dB)

1,8                  13,7

3,5                  14

7                     15

14                   16,2

24                   17

29                   16,3

50                   11,4 

Well done Christophe, best 73!

Fig. 3 -  The schematic diagram.

Fig. 1 - An assembled board, 72 x 25mm

There are SMA connectors for the input and output and an MTA 2-pin connector for the DC power (12V -  14V /40mA max).

2x J310 Push-Pull Low-noise HF pre-Amplifier (500 KHZ - 54 MHZ)

New ears for your HF receiver      FOR MODIFICATION FOR 30 KHZ-30MHZ

                                                                            SEE BELOW

The design is successfully tested with around 15 dB gain from 0.5 to 30 MHZ and still has 8-10 dB gain on more than 55MHZ.

The outupt P1dB is +15dBm and it's noise figure is around 3 dB. The input and the output impedance is 50 Ohms.
This amplifier can be used as a low-noise pre-amplifier in receivers or as a general purpose wideband gain stage.

The two J310 J-FETs are biased at about 20mA each. The input transformer T1 splits the input signal to feed both of the J-FETS in a balanced configuration, while T2 adds the two amplified signals together. This technique improves the 2nd order performance significantly, since all even harmonics cancel out. R1 and L1 form a negative feedback which affects amplifier's gain and frequency response.